“Amazon uses the detailed data it collects on its customers and visitors to create pools of potential marketing targets. Amazon tells Triggit to hunt down particular Web surfers after they’ve left the site, using tracking ‘cookies'; once the startup finds them it purchases ad inventory those users are looking at. Amazon uses that ad space to serve up an ad for the marketer it’s working with, and charges them for the impression.”

What Amazon is doing isn’t actually tracking particular people, but web browsers, and combining that with the information it already has (buying habits, browsing habits within the site, etc.) to create a specific take on the idea of “retargeting” audiences.

According to Triggit’s announcement of the partnership with Amazon, the online retailer plans to offer display advertising across nine ad exchanges and more than four million websites. If people don’t get too upset about the idea of having their browsers potentially followed by Amazon, this could end up being quite the secondary business for the company.